Since yesterday evening my BB gets no connection to our company's BES. The device doesn't show the menu item 'synchronise (now)' in messages. Additionally it doesn't send and receive mails and shows an error message in the browser.
The BES on our server shows the status NO PIN. Activation messages are sent to my email account, but without an access from my BB I'm not able to reactivate the BB.

The device shows an GPRS connection (in capital letters).

I assume the reason for this broken connection is that yesterday I synchronized a colleague's BB on my computer with my email account. When the desktop manager started to synchronize messages, I unplugged the BB. But some of my current email were copied to his device. After I synchronized his device with his mailbox everything worked fine (for him).

Definitely that moment is the last moment which is shown in the BES as the last forwad time.

Up to monday I only have remote access to our BES server.

Can anybody help what I can do now?
Do I have to connect the device by USB an activate it by this way?

Try regenerating a new encryption key...using the Options->Advanced Options->Security section on the device. If your account is still on BES, it should work. If this does not resolve your issue, you may have to remove(delete) your BES account and re-add it to the BES server and activate your BB again.